Most conventional mechanical pumps have issues with reliability due, in part, to the moving components. However, pumps that do not require moving components such as electro-osmotic pumps (EOPs) make them suitable for a variety of applications, including for example “lab-on-a-chip” devices, diagnostic devices, micro total analysis systems (μMTAS), drug delivery systems, and separation and mixing processes, as well as micro-processor cooling systems, to name a few.
Electro-osmosis is used to pump fluids that contain some quantity of charged species, such as positive and negative ions. An electric double layer is a structure that appears on the surface of an object when it is exposed to a fluid. The object might be a solid particle, a gas bubble, a liquid droplet, or a porous body. The electric double layer refers to two parallel layers of charge surrounding the object. The first layer comprises ions adsorbed onto the object due to chemical interactions. The second layer is composed of ions attracted to the surface charge. This second layer is loosely associated with the object. It is made of free ions that move in the fluid under the influence of electric attraction.
Most solid surfaces acquire a surface electric charge when brought into contact with a liquid. When an electric field is applied across the liquid, the ions in the double-layer migrate in the field, which results in viscous drag to create bulk fluid flow and generation of a net pressure. This effect is referred to as electro-osmosic pumping, or EOP pumping. Specifically, EOPs provide fluid flow due to movement of an electric double layer that forms at the solid-liquid interface. Not only do EOPs eliminate moving components, but EOPs also move fluid using the electric field. EOPs can move low conductivity fluids and have a greater pressure and flow rate change when compared to conventional pumps.
Thus, there is a need for low energy mechanical actuators that are of a simple design and construction. The invention satisfies this need.